The present invention relates to a method for measuring a person""s field of vision and, more particularly, to a method for establishing fixation during computerized visual field perimetry such as, for example, where conducted over an Internet website.
In above identified co-pending application, an interactive method and system is disclosed for medical care providers, namely eye care providers, to more effectively target and attract prospective clients by, among other things, affording them eye examinations over an Internet website. To conduct such an examination, stimuli of different shape, size, speed, frequency, location, color, contrast and/or intensity are displayed on the user""s display monitor. Use of such stimuli affords, for example, a convenient manner for conducting computerized visual field perimetry, among other visual tests. A loss of peripheral vision is typically associated with glaucoma, cerebrovascular disease, and pituitary tumors.
In visual field perimetry, the subject""s eye is typically fixated on a stationary target (a xe2x80x9cfixation pointxe2x80x9d) while visual test stimuli are displayed momentarily within the subject""s visual field. The subject""s visual field is then mapped by recording his/her response to each visual test stimulus. To reduce eye fatigue, however, various methods have been developed which use instead a moving fixation point. With respect to such a moving fixation point, selected patents as discussed herein below are of interest, and are incorporated herein by reference.
In U.S. Pat. No. 4,995,717, a fixation point is moved around a computer screen while the subject attempts to track its movement by means of a computer mouse. More particularly, the subject moves the cursor, such as a circle, by means of the mouse to keep the fixation point surrounded by the cursor. Fixation is maintained while the cursor is surrounding the fixation point, allowing test stimuli to then be displayed within the subject""s peripheral vision.
In U.S. Pat. No. 5,565,949, a fixation point again is moved around a computer screen, but during its movement it changes shape, for example, from a circle to a square, or vice a versa. After such a change in the fixation point, the subject is required to press a mouse button. Failure to respond to the change indicates a loss of fixation.
In U.S. Pat. No. 5,737,060, a moving fixation point, such as in the shape of an ant, is displayed on two independent screens of virtual reality glasses, which are worn by the subject. The fixation point is moved around the display screen of the glasses, with its overall direction of movement being clockwise. Two methods of monitoring fixation are used. In one, the subject must respond to changes in the direction of the fixation point though the use of a computer mouse. Any change in direction which the subject does not respond to is considered a loss of fixation. In the second method, blindspot monitoring is used as the fixation control. In this latter case, a target is displayed in the subject""s blindspot on one of the display screens, while the fixation point is displayed on the other screen. If the subject responds to the blindspot target, then there is a loss of fixation since the blindspot target should not have been seen. Otherwise, it is assumed that fixation has been maintained.
Although computerized visual field perimetry systems satisfactorily employ fixation methods, whether stationary or moving, as discussed above herein, it would be desirable to have a method and system for establishing fixation which is less complicated.
The present invention provides a method for establishing fixation during computerized visual field perimetry, requiring the subject to fixate on a stationary target for a brief instance as he/she moves a secondary target towards the stationary target.
In a preferred embodiment, the subject interactively moves the secondary target, for example, in the shape of crosshairs, toward the stationary fixation target displayed on a monitor using the operations of a computer mouse. The stationary fixation target has preferably the shape of a small red circle in order to make it readily identifiable by the subject. The computer mouse pointer when contacted attaches itself to the secondary target. The subject then moves his head so that the fixation target is directly in front of him/her, and, while staring at the fixation target, moves the secondary target towards the stationary fixation target. When the secondary target overlaps the stationary fixation target, it disappears, causing a flashing visual test stimulus to be displayed to the subject for a preset time.
The flashing visual test stimulus appears substantially simultaneous with the overlapping of the secondary target and the fixation target. Fixation is maintained inasmuch as it is unlikely that the subject can cause the overlapping of the crosshairs and the fixation target if he/she is looking away from the fixation target. Once fixation has been established, the subject""s eye is unlikely to wander before the flashing test stimulus is displayed, given that the overlapping and display are almost simultaneous.
As in the conventional perimetry, if the subject observes the flashing visual test stimulus, he/she clicks on one of the mouse buttons, and, afer a slight pause, the secondary target and fixation target reappear on the monitor, preferably at randomly selected positions. Once fixation is again established, the flashing visual test stimulus is displayed at another point within the patient""s visual field, until displayed at all preprogrammed locations determined by the type of visual field perimetry performed.